I love thinking about human psychology. In particular, I love thinking about things humans do that are non-obvious, but pervasively drive their behaviour.
I can think of two general principles that drive a great deal of human behaviour, yet are non-obvious.
The first is that humans have a desire to be superior to others in at least one way. It's possible this is mostly men, but I think it's a useful framework for considering the psychology of men and women. Basically, humans need many dimensions upon which to judge people, such that they are able to judge themselves at the top of at least one dimension.
Imagine a human who is not very good at school and doesn't make much money, but is very piously religious. They can derive self esteem because they have placed themselves at the top of the "religious" dimension They are able to feel good because they have found a dimension upon which they are superior to others.
This sounds cynical but honestly it's a pretty healthy process. People can be dicks about the particular dimension they've chosen to be superior on, but in the end this is fairly universal. And humans need self esteem! So ultimately we should be happy that people have found and identified many creative ways in which to build their own self esteem. To be honest, I wish there were more dimensions & hierarchies, so that more humans could derive high self esteem and contribute positively to society.
If there's any takeaway from this principle, it's that we shouldn't discourage others from deriving their self esteem from something we don't deem "important". Chances are the only reason we don't think their dimension is important is because we've identified an "important" dimension upon which we can deem ourselves superior to others.
The other general principle that I've noticed drives human behaviour is anxiety. Anxiety is pretty well-understood as a human trait, but I don't think it's well-understood as a driver of human behaviour.
For example, I used to work at summer camp and I had one seven year-old child in particular that was incredibly stubborn and difficult to work with. I couldn't understand how he decided when to be stubborn and when to be fun/nice. A coworker suggested to me that this child, who showed no outward anxiety and actually seemed quite confident, was very anxious. This changed my whole relationship with the camper. Once I realized he was anxious, I was able to ignore his stubborn and defiant behaviour, and focus instead on soothing his nerves and reassuring him that I cared about him and that he would be safe. Ultimately, this was more effective at mitigating his stubbornness than simply arguing or being stubborn back. This experience taught me that anxiety can underly behaviour.
There are many examples I've seen since in adults in which anxiety ultimately drives a bad decision by society. I think the best example is gun control. There is a significant percentage of the American population whose decision making is driven by anxiety (rather than what I'd call logic). Because of this, gun control isn't able to take off; anxious people prefer to have a gun on their hip or in their drawer at home. This actually makes me understand anti-gun-control arguments much better; people want a gun to take care of themselves because they're anxious. Unfortunately I haven't figured out how to translate this into an effective argument for gun control, but I think it's fascinating that all my raging against gun control was essentially pointless until I realized that anxiety was the underlying force behind most of the (seemingly irrational) counterarguments I received.
I don't pretend to think that these two principles drive all of human behaviour, but I know that by considering these theories I've come to a better understanding of my fellow humans' arguments. And in the end that's made me more convincing and gotten me that much closer to finding good solutions for problems. I hope I can discover more of these principles and, if you know any, please share them with me :)
Edited to add: an interesting link shared by Paul N in the comments https://www.schneier.com/blog/archives/2006/11/perceived_risk_2.html